The present invention generally relates to methods and apparatus for controlling the registration of regularly reoccurring structural features on one web, tape or strand of continuous material relative to regularly reoccurring structural features on another web, tape or strand of continuous material during joinder. In particular, the invention relates to methods and apparatus for registering modifications (or inserted articles) on a plastic fastener tape relative to thermoformed structures on a plastic packaging material in a thermoform-fill-seal (TFFS) machine.
During the automated manufacture of reclosable packages, a thermoplastic fastener tape unwound from a supply reel or spool is joined (e.g., by conductive heat sealing) to a web of thermoplastic packaging material. The web-to-fastener tape sealing operation can be performed either intermittently (i.e., during dwell times interspersed between intermittent advancements) or continuously (i.e., while the fastener tape and web are advancing continuously).
In cases where a fastener tape without pre-sealing and without sliders must be joined with a web of packaging material having thermoformed troughs or tubs (hereinafter “troughs”), there is a need for the fastener tape to be properly aligned with the web of film (i.e., straightness and cross-machine alignment), but there is no need to register the fastener tape relative to the web in a machine direction. This is due to the fact that the fastener tape has a constant profile along its length and thus has no structural features that need to be registered relative to the troughs thermoformed on the web of packaging material.
The fastener tape typically comprises a pair of continuous zipper strips, each zipper strip having a respective constant profile produced by extrusion. Typically, the respective zipper strip profiles have complementary shapes that allow the zipper strips to be interlocked. These closure profiles may be of the rib-and-groove variety, the interlocking-hook variety or any other suitable fastenable structures. Pre-sealing of the fastener tape involves crushing and fusing the zipper strips at spaced intervals along the fastener tape at locations where the fastener tape will be ultimately cut when each finished package is severed from the work in process. In cases where the fastener tape is pre-sealed before entering the packaging machine, it is important that the pre-seals be properly registered relative to the troughs thermoformed on the web of packaging material.
In cases where sliders are inserted at spaced intervals along the fastener tape before the latter enters the packaging machine, it is common to combine the joinder of the zipper strips at spaced intervals with the formation of slider end stop structures on the fastener tape. Although slider end stops can be placed on or inserted in the fastener tape, it is common practice to simply deform and fuse the thermoplastic material of the zipper strips wherever slider end stops are needed. Typically, the zipper material is softened by applying ultrasonic wave energy and the thus-softened zipper material is shaped to form a slider end stop structure. Typically the slider end stop structure, when bisected, will form back-to-back slider end stops for adjacent packages. The slider end stop structure is formed at a location such that its midplane will be generally coplanar with the plane of cutting when the finished package is severed from the work in process. The plane of cutting, in turn, is typically located midway between successive thermoformed troughs in the packaging material. Thus, it is important that the slider end stop formations on the fastener tape be properly registered relative to the troughs thermoformed on the web of packaging material film.
There is a need for a simple, inexpensive and accurate scheme for controlling the registration of one elongated continuous structure (e.g., plastic fastener tape) with attachments (e.g., sliders) or formed features (e.g., slider end stop structures), as it is fed to a sealing station, where it is joined to another elongated continuous structure (e.g., a web of packaging material) with formed features (e.g., thermoformed troughs). The registration control equipment should also be easy to install.